1. Field of the Invention
The present invention relates to technology of a connector connected to the end of a co-axial cable and a shield cable.
2. Description of the Related Art
Of conventional cables, there are some cables which are equipped with both an internal conductor and an external conductor, for example, a co-axial cable and a shield cable. Connectors to be connected to the end of such cable are those equipped with an internal conductor terminal and an external conductor terminal connected respectively to the end of the internal conductor and that of the external conductor and in which a terminal insulation member comprising an electric insulator lies between the electric connection parts of these terminals.
One example is shown in FIG. 9.
An illustrated cable 10 is provided with an internal conductor 12 and, for example, a braided external conductor 16, in which an insulation layer 14 lies between both conductors 12 and 16 and an exterior of the external conductor 16 is covered with a sheath 18.
On the other hand, a connector connected to the cable 10 is provided with an internal conductor terminal 100, external conductor terminal 110 and terminal insulation member 120.
The internal conductor terminal 100 is provided with an electric connection part 102 fitted into an opposing internal conductor terminal and an internal conductor barrel 104 crimped to the end in such a manner that embraces the end of the internal conductor 12. The external conductor terminal 110 is provided with an electric connection part 112 fitted into an opposing external conductor terminal, an external conductor barrel 114 crimped to the end in such a manner that embraces the end of the external conductor 16 and an insulation barrel 116 crimped to the end in such a manner that embraces the end of the sheath 18. The terminal insulation member 120 is a cylindrical form lying between the electric connection part 102 of the internal conductor terminal 100 and the electric connection part 112 of the external conductor terminal 110, and the internal conductor barrel 104 is provided immediately therebehind.
Incidentally, the thus structured connector is necessary to match the impedance of the connector to that of the cable 10 as much as possible, particularly in sending high-frequency wave electric signals, and insufficiency of such matching will cause a great reflection of the signals and result in disadvantage of a significant decrease in transmission efficiency of the signals. In this instance, an part where electric connection parts 102 and 112 of the connector are overlapped is relatively large in the sectional area, and a terminal insulation member 120 higher in dielectric constant than air lies between the electric connection parts 102 and 112, thereby making it easy to reduce the impedance accordingly and match the impedance with that of the cable 10. In contrast, a part where the internal conductor barrel 104 is crimped to the internal conductor 12 immediately therebehind (hereinafter referred to as “internal conductor crimping part”) is small in the sectional part and the internal conductor barrel 104 is in a condition which is opened outside and surrounded with air, thereby keeping the impedance high and making it difficult to match the impedance with that of the cable 10. Therefore, it is a serious problem in adjusting the impedance at the internal conductor crimping part.
As a means to solve such a problem, JP-A-2001-185302 shown below has disclosed a method in which while an internal conductor crimping part is inserted into a heat-shrinkable tube having an electrically conductive layer inside, the tube is subjected to heat shrinkage and the electrically conductive layer of the tube is closely attached to the internal conductor crimping part, by which the internal conductor crimping part is covered with the tube.